Centrifugal coupling means for photographic cameras provided with a roller-blind type focal plane shutter

ABSTRACT

A centrifugal coupling device for photographic cameras provided with a focal plane shutter of the curtain type for the purpose of providing for uniform exposure over the entire frame, the device is embodied in one of the pairs of rollers which roll and unwind the curtain portion and is arranged to equalize the variations in speed at which the rollers rotate at an exposure.

United States Patent Dahlgren [54] CENTRIFUGAL COUPLING MEANS FOR PHOTOGRAPHIC CAMERAS PROVIDED WITH A ROLLER-BLIND TYPE FOCAL PLANE SHUTTER [72] Inventor: Lennart Gunnar Oskar Dahlgren,

Vastra Frolunda, Sweden [73] Assignee: Fritz Victor Haselblad, Gateborg,

Sweden [221 Filed: Dec. 10, 1969 Appl.No.: 883,747

[30] Foreign Application Priority Data Aug.2l, I969 Sweden ..ll652/69 52 use] .Q ..95/57 511 InLCl. .;.....G03b9l28 5s FieldofSearch ..98/57 3,682,073 [451 Aug. 8, 1972 [56] References Cited I UNITED STATES PATENTS 2,218,248 l0/l940 Mihalyi ..95/57 2,424,439 7/1947 Doyle ..95/57 Primary Examiner-Sarnuel S. Matthews Assistant Examiner-Monroe H. Hayes Att0rney-MGlew and Toren ABSTRACT A centrifugal coupling device for photographic cameras provided with a focal plane shutter of the curtain type for the purpose of providing for uniform exposure over the entire frame, the device is embodied in one of the pairs of rollers which roll and unwind the curtain portion and is arranged to equalize the variations in speed at which the rollers rotate at an exposure.

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lNVE/VTOR Lennort Gunner Oskor Dohlgren ATTORNEYS CENTRIFUGAL COUPLING MEANS FOR PHOTOGRAPHIC CAMERAS PROVIDED WITH A ROLLER-BLIND TYPE FOCAL PLANE SHUTTER portions, and in which the outer shafts run freely on the inner rods, and the inner rods support drums for rolling and unrolling the curtain tensioning means arranged between the outer shafts and the bearings of the inner shafts in the camera housing.

A curtain mechanism of the aforedescribed type presents on one pair of rollers the curtain drive mechanism, which comprises separate spring casings, which during the exposure rolls up the first curtain portion onto the external, tubular shaft or roller and the curtain tensioning means of the other curtain portion onto the drums on the inner rod. The other pair of rollers is provided with means for releasing the first and the second curtain portion and a time setting mechanism which varies the gap width between the first and the second curtain portion, by releasing the second curtain portion at a delay corresponding to the set shutter speed.

There are essentially three reasons why a curtain type shutter of this kind does not provide uniform exposure over the entire frame, and consequently in order to obtain a uniform exposure it is necessary to correct the shutter in different ways.

1. When the shutter is released, the curtain portions are accelerated, and the gap between the curtain portions will passin front of the frame at an increasing speed. It is known to compensate for this by, for example, allowing the gap width to increase correspondingly during its passage in front of the frame which can be effected by suitable design of the rollers onto which the tensioning means of one or the other curtain portion is wound.

2. The bending resistance of the curtain material renders it necessary to supply more energy when rolling the curtain portions onto the outer rollers, this energy boost being recovered to a corresponding extent when unrolling the said curtain portions. During the exposure, the first curtain portion is rolled up and the other is unwound by their respective rollers, which means that the first portion of the curtain will move slightly slower and the other curtain portion slightly faster than intended. The consequence of this is that the gap width tends to decrease progressively during the exposure sequence, this error being added to the error mentioned under point 1. It is known to compensate this error source partly by prebending the curtainportions and partly by tensioning the spring casing of the rolled curtain portion to a slightly greater extent than in the unrolled portion.

3. A varying friction resistance in the mechanism and possible tendencies of the curtain portions to become askew cause haphazard interferences in the required smooth passage of the curtain. Attempts have been made to restrict the jerky, intermittent, passage of the curtain by embodying close tolerances and/or finely machined running surfaces.

Despite these known arrangements for correcting and avoiding occurring deviations in the uniform exposure of the frame, certain errors still remain which, even in the case of high quality curtain type shutters, are so great that scope is found for further improvements in this respect.

The means of invention mainly counteracts the nonuniform speed of the curtain portions presented under point 3, although it also contributes towards equalizing the difference in the speeds at which the curtain portions move. The invention relates to a centrifugal coupling means, suitably built into the driven pair of rollers, between the inner rod and outer roller thereof. Tests have shown that the equalization of the irregularities in movement and passage of the curtain type shutter achieved by means of the present invention is of such high standard that any remaining deviations from an absolute uniform passage in no way detract from those requirements placed upon a curtain type shutter of high quality. The invention is mainly characterized in that one roller pair, preferably the driven pair, is provided with a centrifugal coupling built in between the inner and the outer roller, for the purpose of equalizing variations occurring during the exposure between the speed at which the outer and the inner roller rotate.

A preferred embodiment of the invention and a number of variations in design will now be described in more detail with reference to the appended drawings, in which FIG. 1 shows a diagrammatic view of a curtain type shutter of the invention, seen obliquely in plan,

FIG. 2 shows the roller pair driven by spring casings, with the outer roller partially cut away,

FIG. 3 shows the roller pair actuated by the release mechanism with the outer roller partially cut away, and

FIGS. 4, 5 and 6 show in detail alternative embodiments of the centrifugal coupling means.

FIG. 1 shows diagrammatically the principle construction of a curtain type shutter having concentric pairs of rollers, in which a centrifugal coupling means according to the invention is embodied. The curtain type shutter is mounted close to the rear side 1 of the camera housing, in front of the partially hidden frame 2. The roller pairs are journalled in the upper side 3 of the camera housing and in the bottom 4 thereof, said bottom portion also supporting the curtain mechanism spring motors mounted in spring casings 5, 6 and the release mechanism for the curtain shutter, said mechanisms being shown as cog wheels 7, 8 with latching means which are actuated by electromagnets 9, 10. The first curtain portion 11 is attached to the outer roller 12 on the right-hand pair of rollers in FIG. 1, and the curtain tensioning means 13 of the curtain portion 11 is attached to the drums 14 on the inner, hidden rod 15 of the left-hand pair of rollers as seen in the Figure. The other curtain portion 16 is attached to an outer roller 17 on the left-hand pair of rollers in the Figure, and the tensioning means 18 of the curtain portion 16 is attached to the drums 19 on the inner, hidden rod 20 of the right-hand roller pair. Prior to making an exposure, when the shutter is cocked the second curtain portion 16 is completelyrolled up on the outer roller 17 and the first curtain portion covers the frame 2 and its free edge 21 reaches almost up to the free edge 22 of the second curtain portion located on the outer roller 17. The distance between the free edges 21, 22 of the curtain portions corresponds in this position by the highest shutter speed obtained when the two curtain portions ll, 16 are released simultaneously.

By means of a shutter speed selection mechanism (not shown) the second curtain portion 16 can be released at a later point of time which corresponds to the desired exposure speed, whereby the width of the gap between the free edges 21, 22 of the curtain portions 11, 16 increases to a corresponding extent. In the position of the curtain portions 11, 16 shown in FIG. 1, the width of the gap during the illustrated exposure is relatively large, i.e., affords a slow shutter speed. Upon completion of the exposure, the frame is covered by the second curtain portion 16. The roller pair to the right in FIG. 1 is shown in FIG. 2, with an embodiment of the centrifugal means embodied between the outer shaft or roller 12 and the inner rod 20. Located in the upper side 3 of the camera housing and the bottom portion 4 are fixed bearings 23, 24 for the inner rod 20, the inner rod supports drums 19 situated close to the bearings 23, 24 and intended for the tensioning means 18 of the second curtain portion 16, and bearings 25 which support the outer, tubular roller 12. The rollers 12, and inner rod 20 support present fixed gears 26, 27 which engage pinions on the spring casings 5, 6. The centrifugal coupling means comprises a shaft 29, which can either be stationarily secured in a bore 28 in the inner rod 20 or be freely movable therein. The length of the shaft 29 is slightly shorter than the internal diameter of the outer roller 12 and on the free ends of the shaft 29 are mounted freely movable centrifugal weights 30. FIG. 3 illustrates the second roller pair, which is provided with gear wheels 31 and 32 engaging with the cog wheels 7 and 8, which are latched by the electromagnets 9, 10. This roller pair is principally constructed in the same manner as that on the opposite side, but lacks the centrifugal coupling means. When the curtain shutter is released, electromagnet releases the inner rod 15, whereupon the first curtain portion 11 begins to move and the outer roller 12 and the inner rod l5 are caused to rotate. The centrifugal coupling means is inoperative until the electromagnet 9 releases the outer roller 17 at a delay corresponding to the set shutter speed, whereupon the second curtain portion 16 begins to move and all of the outer rollers l2, l7 and the inner rods 15, 20 rotate. The centrifugal weights 30 are then flung out towards the inside of the roller 12 and cause the roller 12 and inner rod 20 to be interconnected, thereby equalizing any variations in the speed at which the roller and inner rod rotate, which results in a more uniform passage of the curtain type shutter.

In the exemplary embodiment of FIG. 4,- the inside of the outer roller 12 at the portion of the surface thereof which contacts the centrifugal weights 30 is provided with a roughened surfacestructure, or also is provided with a coating 33 to increase friction.

12 is to provide them with compression or tension springs 35. It is possible by applying the alternative embodiment exemplified in FIGS. 4, 5 and 6, either individually or in any combination, to adjust the action of the centrifugal coupling means so that the smoothest possible passage of the curtain is obtained.

The invention is not restricted to the illustrated embodiments, but can be varied within the scope of the invention, for example by embodying the centrifugal coupling means in the roller pair consisting of inner rod and outer roller 17 actuated by the release means or by changing the structure or guide means of the cen- A corresponding effect is obtained in the exemplary trifugal weights, etc.

What is claimed is:

l. A centrifugal coupling device for a photographic camera having a focal plane shutter of the curtain type comprising a housing forming a frame, roller means situated on the opposite sides of the frame, curtain portions arranged to be rolled on said roller means, curtain tensioning means attached to said curtain portions and arranged to be rolled on said roller means, said roller means comprising two pairs of rollers each located on an opposite side of said frame, each said pair of rollers comprising an inner rod and an outer tubular roller concentrically arranged about and freely rotatably mounted on said inner rod, bearings for rotatably mounting said inner rod, drums fixed to said inner rod for rotation therewith for rolling and unrolling said curtain tensioning means, said drums located between the ends of said outer tubular roller and said bearings, said outer tubular roller arranged to roll and unroll said curtain portions, wherein the improvement comprises that a centrifugal coupling is incorporated in one of said pairs of rollers and extends between said inner rod and said outer tubular roller for equalizing variations occurring during exposure between the speeds at which the outer tubular roller and inner rod rotate.

2. A centrifugal coupling device, as set forth in claim 1, wherein said inner rod has a radial bore extending therethrough, a shaft positioned within and extending through the radial bore in said inner rod and the length of said shaft being less than the inner diameter of said outer tubular roller, and freely running centrifugal weights arranged on the free ends of said shaft so that upon rotation of said inner rod said weights are caused to abut against the inside surface of said outer tubular roller in order to interconnect by friction said outer tubular roller and said inner rod so that any variation in the rotational speed between the two rotating in the same direction is-substantially equalized.

3. A centrifugal coupling device, as set forth in claim 2, characterized in that the surfaces of said centrifugal weights which contact the inside surface of said outer tubular roller are coated with a material presenting a high coefficient of friction.

4. A centrifugal coupling device, as set forth in claim 2, characterized in that at least the portion of the inner surface of said outer tubular roller which is arranged to be contacted by said centrifugal weights is provided with a roughened surface for the purpose of increasing the friction between the contact surfaces of said centrifugal weights and the inner surface of said outer tubular roller.

5. A centrifugal coupling device, as set forth in claim 2, characterized in that the inner surface of said outer 6 trifugal weights, and said springs arranged for one of increasing and decreasing the contact pressure between said centrifugal weights and the inner surface of said outer tubular roller. 

1. A centrifugal coupling device for a photographic camera having a focal plane shutter of the curtain type comprising a housing forming a frame, roller means situated on the opposite sides of the frame, curtain portions arranged to be rolled on said roller meaNs, curtain tensioning means attached to said curtain portions and arranged to be rolled on said roller means, said roller means comprising two pairs of rollers each located on an opposite side of said frame, each said pair of rollers comprising an inner rod and an outer tubular roller concentrically arranged about and freely rotatably mounted on said inner rod, bearings for rotatably mounting said inner rod, drums fixed to said inner rod for rotation therewith for rolling and unrolling said curtain tensioning means, said drums located between the ends of said outer tubular roller and said bearings, said outer tubular roller arranged to roll and unroll said curtain portions, wherein the improvement comprises that a centrifugal coupling is incorporated in one of said pairs of rollers and extends between said inner rod and said outer tubular roller for equalizing variations occurring during exposure between the speeds at which the outer tubular roller and inner rod rotate.
 2. A centrifugal coupling device, as set forth in claim 1, wherein said inner rod has a radial bore extending therethrough, a shaft positioned within and extending through the radial bore in said inner rod and the length of said shaft being less than the inner diameter of said outer tubular roller, and freely running centrifugal weights arranged on the free ends of said shaft so that upon rotation of said inner rod said weights are caused to abut against the inside surface of said outer tubular roller in order to interconnect by friction said outer tubular roller and said inner rod so that any variation in the rotational speed between the two rotating in the same direction is substantially equalized.
 3. A centrifugal coupling device, as set forth in claim 2, characterized in that the surfaces of said centrifugal weights which contact the inside surface of said outer tubular roller are coated with a material presenting a high coefficient of friction.
 4. A centrifugal coupling device, as set forth in claim 2, characterized in that at least the portion of the inner surface of said outer tubular roller which is arranged to be contacted by said centrifugal weights is provided with a roughened surface for the purpose of increasing the friction between the contact surfaces of said centrifugal weights and the inner surface of said outer tubular roller.
 5. A centrifugal coupling device, as set forth in claim 2, characterized in that the inner surface of said outer tubular roller arranged to be contacted by said centrifugal weights is coated with a material presenting a high coefficient of friction.
 6. A centrifugal coupling device, as set forth in claim 2, characterized in that springs are positioned on said shaft extending between said inner rod and said centrifugal weights, and said springs arranged for one of increasing and decreasing the contact pressure between said centrifugal weights and the inner surface of said outer tubular roller. 